CAMBRIDGE, Mass. — After a grueling second day of intense and graphic questioning by a defense lawyer, the man who has accused defrocked priest Paul Shanley of raping him as a child broke down on the witness stand Thursday and begged the judge not to force him to continue testifying.

“I can’t do this again,” the man said, his shoulders slumped and his head down as Shanley’s attorney asked graphic questions about the nature of the alleged abuse. “I can’t start over again.”

At one point during the questioning, the accuser loudly sobbed as he clasped his hands behind his head and pressed his forehead against the rail of the witness stand.

Frank Mondano, Shanley’s attorney, has spent the past two days seeking to undermine the accuser’s credibility, grilling him about his troubled childhood, his abuse of alcohol and steroids, his gambling habit — and his motivation for coming forward with what he says are repressed memories of the alleged abuse.

Mondano has said the man made up his story to cash in on the multimillion-dollar settlements paid to victims of abuse by priests in Boston’s Roman Catholic Archdiocese.

The accuser, now a 27-year-old firefighter, says Shanley raped and molested him at a parish outside Boston beginning when he was

6. He didn’t remember the abuse until early 2002, when he heard a friend’s account of being abused as a boy by Shanley.

The man is the lone remaining accuser in the case against the 74-year-old Shanley, one of the central figures in the Boston clergy sex abuse scandal. His case became one of the most notorious in the scandal because personnel records showed that church officials knew Shanley publicly advocated sex between men and boys, yet continued to transfer him from parish to parish.

By the end of the day Thursday, doubts were being raised about the likelihood the accuser would return for a third day of questioning by Mondano. The judge urged him to return, but is unable to force him to continue testifying because he is not appearing under a subpoena.

“Can I ask a request of you?” the man told the judge. “Please don’t make me.”

Afterward, Mondano told reporters that if the accuser does not show up for further questioning, he believes he has grounds for a mistrial — or the basis for asking a judge to declare Shanley not guilty on the grounds he wasn’t able to fully confront his accuser.

Earlier in the day, the accuser said his mother left him when he was 3 years old, and his father beat him. Under a barrage of questions from Mondano, he also acknowledged that he drank heavily and abused steroids for 8 years starting when he was 16. He also said he gambled away hundreds of dollars at a time.

He blamed his steroid use on Shanley, saying the sexual abuse caused him to develop a “poor self image.”

“It just made me feel better about myself,” said the accuser, who said he once smuggled steroids across the border from Mexico. “I just thought I looked better.”

Plaintiffs in the hundreds of lawsuits filed over the clergy sex abuse scandal have made similar claims that they spiraled into lives of drug abuse and depression after being molested by Catholic priests.

Shanley faces three charges of raping a child and two charges of indecent assault and battery on a child. He could get life in prison if convicted.